Storage of soil samples leads to over-representation of the contribution of nitrate to plant-available nitrogen

Abstract

Delays between soil sampling and processing for analysis are common in both research and agronomy, but the effects of storage conditions on measurements of plant-available nitrogen (N) are rarely considered. With increasing recognition of organic N pools in soils, such as amino acids and peptides, it is necessary to determine how sample handling impacts the outcomes of soil N quantification. In this study, we used in situ microdialysis to approximate plant availability of amino acids, ammonium and nitrate, then compared to both potassium chloride (KCl) extract and microdialysis samples taken from excavated soil samples when in the field, after 24h refrigerated storage, and after storage for 1month, either refrigerated or air-dried. Nitrate levels measured with microdialysis and KCl extracts increased immediately after soil sampling and continued to accumulate in the next day and 1month stored samples. Amino acid and ammonium measurements remained more constant; however, microdialysis showed a decline in amino acid-N between in situ and next day samples. The proportional representation of N pools in the in-field extracts was most similar to in situ microdialysis.Soil samples should be processed for N analysis as close to sampling as possible, and the storage duration and conditions reported. The influence of storage must be considered in interpreting soil test results.

Mycorrhizal symbiosis pathway and edaphic fertility frame root economics space among tree species

“…All soil samples were sieved (2‐mm mesh) to remove roots and visible organic particles and stored at 4°C for later laboratory analysis. Soil samples were generally extracted and analysed within 1–2 wk after sampling to minimize the influence of storage time on available nutrients (Bailey et al ., 2022).…”

Soil sample storage conditions affect measurements of pH, potassium, and nitrogen

“…Andrews et al (2004) define SQIs as "those soil properties and processes that have greatest sensitivity to changes in soil function " (p. 1945). While in situ testing of soils in the field might give the most accurate results (Bailey et al, 2021), it is not always feasible from a practical and logistical perspective. The alternative to in situ testing involves the removal of soil samples to the laboratory and the subsequent use of wet-chemistry techniques to analyze the soil physiochemical properties.…”